THE PREPARATION OF DICARBONYLS

Abstract: A method for the production of 1,3-diketones and 1,3-ketoesters of formula (1), (2), (3) or (4), which comprises converting the corresponding compound of formula (5), (6), (7) or (8), into compounds of formula (1), (2), (3) or (4) by reaction with elemental fluorine, wherein R1 is selected from alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl and acetoxy, R2 is selected from hydrogen, halogen, nitro, cyano, alkyl, cycloalkyl, acetoxy and aryl substituted alkyl, acetoxy, aryl and substituted aryl, and R3 is selected from alkyl, substituted alkyl, oxyalkyl and substituted oxyalkyl, R4 and R5 are hydrogen or alkyl, n is an integer in the inclusive range 1 to 8 and the structures represented by formulae (2), (3), (4), (6), (7) and (8) are cyclic.

Description: The preparation of dicarbonyls The present invention relates to the preparation of dicarbonyls, in particular dicarbonyl compounds which are 2-fluoro- and 2, 2-difluoro-1, 3-diketones and -ketoesters. The use of elemental fluorine for the site specific fluorination of aliphatic compounds is rarely satisfactory due to the high reactivity of the element which leads to unspecific multiple substitution, carbon-carbon bond cleavage and oxidation. Because of the growing importance of fluorinated organic compounds in applications such as in biochemical systems, (Ref 1: R Filler, Y Kobayashi (editors) ; Biomedical Aspects of Fluorine Chemistry; Elsevier Biomedicinal Press, New York, 1982), (Ref 2: J T Welch; Tetrahedron, 1987, 43, (14) , 3123) in recent years considerable effort has gone into finding ways of introducing fluorine into specific sites within molecules to provide building blocks for the preparation of biologically active compounds which have more complex structures. In this context, the replacement of the 2 hydrogen in 1, 3-diketones and 1, 3-ketoesters is just one transformation that has aroused much interest since the mono- and/or di-fluorinated products can be useful intermediates in the preparation of bio-active molecules. This transformation has been carried out either by treating the 1,3-diketone or 1, 3-ketoester or their metal enolates with one of several "electrophilic fluorinating agents" that have been developed recently. For example, 1,3-diketones and 1,3-ketoesters have been treated with acetyl hypofluorite (Ref 3: S Rozen and 0 Ler an; J. Org. Chem. , 1983, 48, 724), N-fluoro-pyridinium salts with or without a Lewis Acid catalyst (Ref 4: T Umemoto et al; J Amer. Chem. Soc. , 1990, 112, 8563), xenon difluoride (Ref 5: B Zajc and M Zupan; J Chem Soc, Chem Commun, 1980, 759), lamellar C 19 XeF 6 (Ref 6: H B Kagan, S S Yemul and R Setton; Tetrahedron Letts., 1980, 21, 277), and N- fluorobis[ (perfluoroalkyl) sulphonyl] imides (Ref 7: G Resnati and D D Desmarteau; J Org. Chem., 1992, 57, 4281) (Ref 8: Z Xu, D D Desmarteau and Y Gotoh; J Fluorine Chem., 1992, 58, 71), (Ref 9: G Resnatti and D D Desmarteau; J. Org. Chem., 1991 56, 4925), (Ref 10 Z Xu, D D Desmarteau and Y Gotoh; J Chem Soc; Chem. Co mun; 1991, 179) and their metal enolates have been treated with acetyl hypofluorite (Ref 3) , N-fluoro-pyridinium salts (Ref 4) . Thus, although the treatment of 1, 3-diketones and 1,3- ketoesters with electrophilic fluorinating agents can sometimes give high yields of the required mono- or di- fluorinated products, some of these reagents decompose fairly quickly, and the compounds from which they are made are often expensive or difficult to obtain. According to the present invention there is provided a method for the production of 1, 3-dicarbonyls of formula (1) , (2), (3) or (4) as follows: R 1 COCFR 2 COR 3 (1) (CH 2 ) n COCFCOR 3 (2) (CR 4 R5) n COCFR 2 CO (3) (CR 4 R 5 ) n -CF.COCH 3 (4) L I i \∞ which comprises converting the corresponding compound of formula (5), (6), (7) or (8) as follows: R COCHR2COR- (5) (CH 2 ) n COCHCOR 3 (6) (CR 4 R 5 ) n COCHR 2 CO (7) (CR 4 R 5 ) n -CH.CO.CH 3 (8) I J 0 CO into compounds of formula (1) , (2) , (3) or (4) by reaction with elemental fluorine, wherein R*L is selected from alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl and acetoxy, R 2 is selected from hydrogen, halogen, nitro, cyano, alkyl, cycoloalkyl, acetoxy and aryl substituted alkyl, acetoxy, aryl and substituted aryl, and R 3 is selected from alkyl, substituted alkyl, oxyalkyl and substituted oxyalkyl, R 4 and R5 are hydrogen or alkyl n is an integer in the inclusive range 1 to 8 and the structures represented by formula (2), (3) , (4), (6), (7) and (8) are cyclic. Where any one of the groups R^, R 2 and R 3 is an alkyl, cycloalkyl or aryl group the group may include one or more optional substituents or hetero atoms. Where R 2 in formula (5) is hydrogen, R 2 in formula (1) may be fluorine so that the product has formula (9) as follows: R-LCOCF2COR-3 (9) Where R 2 in formula (7) is hydrogen, R 2 in formula (3) may be fluorine so that the product has the formula (10) as follows: C (R 4 R 5 ) n -COCF 2 CO (10) Fluorine itself has been rarely used for the conversion of 1, 3-diketones or 1, 3-ketoesters or their derivatives into the corresponding 2-fluorocompounds in the prior art. However, trimethyl silyl ethers of 1,3- diketones and 1,3-ketoesters have been converted by reaction with fluorine into the corresponding 2-fluoro- 1, 3-diketones and 2-fluoro-1, 3-ketoesters in good yields but only at low (-78°C) temperature and in a solvent (CFC1 3 ) which is to be phased out under the terms of the Montreal Protocol (Ref 11: S T Purrington, C L Bumgardner, N V Lazaridis and P Singh; J. Org. Chem., 1987, 52, 4307) . Surprisingly, we have now found that fluorine itself can be used to convert 1, 3-diketones and 1, 3-ketoesters into the corresponding 2-fluoro or 2,2-difluoro compounds in high yield and without the above disadvantages and this beneficially allows 1, 3-diketones and 1,3-ketoesters of commercial value to be produced by a relatively simple and convenient route. The process according to the present invention may be carried out by passing fluorine gas into a solution of the appropriate compound of formula (5) , (6) , (7) or (8) in a substantially inert solvent, eg a neutral substance such as acetonitrile or water, an acid such as formic acid or a mixture of neutral and/or acid solvents. Desirably, the solvent overall is acidic ie pH <7. We have found that use of formic acid optionally together with trifluoracetic acid is especially preferred. In particular, formic acid forming from 70 to 90 per cent by volume in a mixture with trifluoracetic acid is particularly suitable. This gives a cleaner reaction than use of acetic acid plus sodium acetate in an essentially basic medium as used in the prior art. Such a medium produces fluorination via the hypofluorite rather than fluorine itself. The reaction may be carried out in a vessel in which the solution is present or alternatively a flowing stream of the solution may be contacted with a gaseous flow of fluorine in countercurrent fashion. The reaction of the process may be carried out at a temperature in the range -60°C to +150°C although a temperature of from -20°C to +50°C is preferred. The fluorine gas is preferably diluted before use by mixing with an inert gas such as nitrogen or helium. The concentration of fluorine in inert gas is preferably from 1 per cent to 50 per cent by volume, preferably from 2 per cent to 25 per cent by volume, especially 5 per cent to 15 per cent by volume. The ratio of fluorine to compound of formula (5) , (6) , (7) or (8) may be varied within wide limits although it is preferred that the molar ratio is in the range 0.5 to 4.0:1, especially 1.1 to 2.5:1 (fluorine : organic compound) . When fluorination is complete the fluorinated product in the process according to the present invention may be isolated by purging the reaction mixture with inert gas to remove any residual fluorine gas and hydrogen fluoride followed by dilution with excess water or aqueous solution and extraction into a suitable solvent followed by distillation. Thus the present process according to the present invention provides an inexpensive and convenient synthetic route to 2-fluoro- and 2,2-difluoro -1, 3-diketones and - 1, 3-ketoesters. Embodiments of the present invention will now be described by way of example only with reference to the following Examples. Example 1 Fluorination of Ethyl 2-cyclohexanone carboxylate Through a stirred solution of ethyl 2-cyclohexanone carboxylate (4.25gm., 0.025m) in formic acid (50ml) was bubbled fluorine (0.05m), diluted with nitrogen to 10% fluorine, over 2 hours. The internal temperature was maintained in the range 4-8°C. When the reaction was complete, the vessel was purged with nitrogen and the contents were poured into water and extracted with dichloromethane. The solvent was removedd from the dried (MgS0 4 ) extracts to yield ethyl 2-fluoro-2-cyclohaxanone carboxylate, identified by its retention time which was coincident with that of an authentic sample, its NMR spectra [ 19 F(CDCl 3 )δ F = -161.24ppm (t) J HF = 16.4 Hz.], and Mass Spectrum (El) [188, (M + ) ] . Two small peaks in the gas chromatogram with longer retention times that the main product were recognised as 1) starting material, and 2) a compound with a molecular mass of 206 which corresponds to a molecular formula of CgH 1 F 2 θ3. Conversion from ethyl 2-cyclohexanone carboxylate, 95%; Yield, 90%. Example 2 Fluorination of Ethyl-2-cvclohexanone carboxylate This example was carried out in a similar manner to that described in Example 1, except that the solvent was acetonitrile and the temperature was maintained at about - 10°C. Work up gave ethyl 2-fluoro-2-cyclohexanone carboxylate in 70% yield and C9Hι 2 F 2 0 3 in a ca.8% yield. The conversion was ca.90%. Example 3 Fluorination of Ethyl-2-cyclohexanone carboxylate This example was carried out as in Example 1 except that solvent consisted of a mixture of formic acid (40ml) and water (10ml) , and the reaction temperature was maintained at ca.lO°C. The yield of ethyl 2-cyclohexanone carboxylate was 95% and the conversion was 90%. Example 4 Fluorination of Ethyl-2-oxocyclopentane carboxylate Ethyl-2-oxocyclopentane carboxylate (3.9gm 0.025m) was fluorinated in a similar manner to that described in Example 1. Work up gave ethyl-2-fluoro-2-oxocyclopentane carboxylate [NMR(CDC1 3 ) ; 19 F, δ F = -164.6 ppm (t) J HF = 21.0 Hz. MS (El); M + 174]. Yield 56%. Also recognised in the reaction mixture was cyclopentanone [M.S. (El); 84 (M + ) ] , unreacted starting material, and diethyl adipate [M.S. (CI) ; 203 (M+l) + ]. Conversion 80%. Example 5 Fluorination of Ethyl acetoacetate The fluorination of ethyl acetoacetate (3.25gm, 0.025m) was carried out in a similar manner to that described in Example 1 except that the fluorine (0.05m) was passed through the reaction mixture over a period of 4 hours and the reaction temperature was maintained at ca. 10°C. Work up gave ethyl 2-fluoroacetoacetate [NMR(CDC1 3 ); 19 F , δ F = -193.70 ppm (dq) J HF = 49.4 Hz, J HF = 12.1 Hz M.S. (El) ; 148 (M + ) ] . A small singlet in the reaction product at -114.7 ppm was attributed to ethyl 2,2-difluoroacetoacetate. A small doublet at -204.5 ppm (J HF = 43.0 Hz) and triplet of equal intensity at -235.8 ppm ( HF = 45.3 Hz ) were attributed to ethyl 2-fluoro-2- (fluoroacetyl)acetate. Total Yield, >90%. Conversion, 90%. Example 6 Fluorination of Ethyl 2-chloroacetoacetate The fluorination of ethyl 2-chloroacetoacetate (4.1 gm, 0.025m) was carried out in a similar manner to that described in Example 1 except that the temperature was maintained in the range 10-15°C. Work up gave ethyl 2- chlcro-2-fluoroacetate [NMR (CDCI 3 ) ; *-*H, δ H = 4.39 ppm (q, J HH = 7.3Hz, CH 3 CH 2 ) , 2.46 ppm (d, J HF = 2.6 Hz, CH 3 CO) , 1.36 ppm (t, J HH = 7.1 Hz, CH 3 CH 2 ) ; 19 F, δ F = -123.5 ppm (J HF = 2.4 Hz) : MS (El); 183 (M+l) ] . A small broad singlet at -127.6 ppm and triplet of doublets at -234.7 ppm ( HF = 46.3 Hz, J FF = 1.9 Hz) were attributed to ethyl 2-chloro-2-fluoro-2-(fluoroacetyl)acetate. Conversion of starting material to product was ca. 15% and the yield was ca. 90%. Example 7 Fluorination of ethyl 2-chloroacetoacetate This experiment was carried out in a manner similar to that in Example 6 except that 1.9gm of sodium formate was added to the reaction mixture. This has the effect of increasing the conversion to 45%. The yield and nature of the product were similar to those in Example 6. Example 8 Fluorination of ethyl 2-methylacetoacetate The fluorination of ethyl 2-methylacetoacetate (3.6gm, 0.025m) was carried out in a manner similar to that described in Example 6. Work up gave Ethyl 2-fluoro-2- methylacetoacetate [NMR (CDC1 3 ) ; 19 F, δ F = -157.7 ppm (q- q, J HF = 22.1 Hz, J HH = 4.5 Hz) : MS (El); 163 (M+l)]. A small quartet of multiplets at -166.6 ppm (JHF = 23.2 Hz) and triplet of doublets at -236.0 ppm (JHF = 4*5.,7 Hz, J = 3.7 Hz) in the reaction product were attributed to ethyl 2-fluoro-2-(fluoroacetyl) -2-methyl acetate. Conversion of starting material to product was ca. 25% and the yield was ca. 90%. Example 9 Fluorination of 2-Acetyl butyrolactone The fluorination of 2-Acetyl butyrolactone (3.2gm, 0.025m) was carried out in a manner similar to that described in Example 6. Work up gave 2-fluoro-2-acetyl butyrolactone(nc) [NMR (CDC1 3 ) ; 1 H, δ H = 4.5 ppm (m) , 2H; 2.87 ppm ( ) , 1H; 2.55 ppm (m)lH; 2.47 ppm (d) , J HF = 5.0 Hz, 3H; 19 F, δ F = -163.4 ppm (ddqd) , J = 11.8, 11.8, 4.9, and 1.5 Hz]. Accurate mass measurement:- Found (CI, methane) , 147.0442; C 6 Hs0 3 F requires 147.0457]. A small multiplet at -173.8 ppm and triplet of doublets at -237.9 ppm (Jtriplet = 46.3 Hz, Jdoublet = 6-8 Hz) in the reaction product were attributed to 2-fluoro-2- (fluoroacetyl) butyrolactone. The conversion was ca. 70% and the yield was ca. 85%. Example 10 Fluorination of Ethyl 4-chloroacetoacetate The fluorination of ethyl 4-chloroacetoacetate (4.1 gm, 0.025m) was carried out in a manner similar to that described in Example 6. Work up gave ethyl 2-fluoro-4- chloroacetoacetate(nc) [NMR (CDC1 3 ) ; 19 F, δ F = 198.8 ppm (td) , J HF = 48.5 Hz and JH F = 3.3 Hz. Accurate mass measurement:- Found (CI, methane), 183.0178; C 6 Hg0 3 ClF requires 183.0224]. Example 11 Fluorination of 2 ,4-Pentanedione Through a stirred solution of 2,4-pentanedione (2.5gm, 0.025m) in formic acid (50ml) was bubbled fluorine (0.05m) , diluted with nitrogen to 10% fluorine, over 2 hours. The internal temperature was maintained in the range 10-15°C. When the reaction was complete, the vessel was purged with nitrogen and the contents were poured into water and extrated with dichloromethane. The solvent was distilled from the dried MgS0 4 ) extracts to yield 3- fluoro-2,4-pentanedione [NMR(CDC1 3 ); 1 H, δ H = 5.25 ppm (d, J HF = 50.0 Hz, CHF) , 2.31 ppm (m, keto 2xCH 3 ) , 2.18 ppm ( , enol 2xCH 3 ) ; 19 F, δ F = -192.0 ppm (dm, J HF = 49.2 Hz, keto ca, 6.5 parts) and -173.7 ppm (s, enol ca. 1 part) . MS (El); 118, (M + ) ] . Also detected in the reaction product was a small singlet at -115.4 ppm which was attributed to 3, 3-difluoro-2 ,4-pentanedione [MS (El) ; 136 (M + ), 94(M + -CH 2 CO) ] , and a doublet at -204.0 ppm (J HF = 42.4 Hz) and triplet of doublets at -236.6 ppm (J HF = 46.2 Hz, J FF = 2.8 Hz) which were attributed to 1,3-difluoro- 2,4-pentanedione [MS (El); 136(M + ), 103 (M + -CH 2 F) ] . Conversion, 90%; Total Yield, 85%. Example 12 Fluorination of 2 ,4-Pentanedione In a similar reaction to that described in Example 11, fluorine (0.28m) was passed through a solution of 2,4- pentanedione (0.113m) in formic acid (225ml) over a period of 18 hours. The reaction product was mainly 3-fluoro- 2,4-pentanedione, with much smaller amounts of 3,3- difluoro-2,4-pentanedione and 1, 3-difluoro-2 , 4- pentanedione. Conversion, 100%. Example 13 Fluorination of 3-Methyl-2 ,4-pentanedione In a similar reaction to that described in Example 11, fluorine (0.05m) was passed through a solution of 3- methyl-2,4-pentanedione (0.025m) in formic acid (50 ml) . The main product was identified as 3-fluoro-3-methyl-2 ,4- pentanedione [NMR(CDC1 3 ) ; 1 H, δ H = 1.6 ppm (3H, d, J HF = 22 Hz, CFCH 3 ), 2.3 ppm(6H, d, CH 3 ) , J HF = 3.2 Hz; 19 F, δ F = -158.0 ppm (q, J = 22 Hz) . MS (El); 133(M + +1), 90(M + - CH 2 C0) , 43(CH 3 CO)]. Also produced in the reaction was ca. 10% of 1,3-difluoro-3-methyl-2 ,4-pentanedione [NMR(CDC1 3 ); 19 F, δ F = 166.1 ppm (q, J HF = 23 Hz) , -235.3 ppm (t, J HF = 46.5 Hz) . MS (El) ; 150 (M + ), 61(CH 2 FCO), 43(CH 3 CO)]. Conversion, 90%; Yield (monoF) , 80%. Example 14 Fluorination of 3-Chloro-2 ,4-pentanedione In a similar way to that described in Example 11, fluorine (0.05m) was passed through a solution of 3- chloro-2,4-pentanedione (0.025m) in formic acid (50ml) over a period of 2 hours. The product was identified as 3-chloro-3-fluoro-2,4-pentanedione [NMR(CDC1 3 ) ; ^-H, δ H = 2.4 ppm (d, J HF = 3 Hz); 19 F, δ F = -126.2 ppm (septet, J HF = 3 Hz) . MS (El); 152 (and 154) (M + ) , 117 (M+-C1) , 110 (M + -COCH 2 )]. A singlet with δ F - 129.3 ppm and triplet at δ F = -233.8 ppm of equal intensity in the 19 F NMR of the product was attributed to 1, 3-difluoro-3-chloro-2,4- pentanedione. Conversion, 85%; Yield 70%. Example 15 Fluorination of 2-Acetylcylohexanone In a similar way to that described in Example 11, fluorine (0.05m) was passed through a solution of 2- acetylcyclohexanone (0.025) in 50 ml formic acid over a period of 2 hours. The main product was identified as 2- acetyl-2-fluorocyclohexanone [NMR(CDC1 3 ) ; 19 F, δ F = -157.8 ppm. MS (El); 158 (M + ) , 116 (M+-COCH 2 )]. Also detected in the reaction product was 2-(fluoroacetyl) -2- fluorocyclohexanone [NMR(CDCl 3 ) ; 19 F, δ F = -168.8 ppm (m) and -236.9 ppm (td) , J HF = 46.8 ppm, J FF = 7.3 Hz MS (El); 176 (M + ) ] . Conversion, 95%; Yield (monoF) , 80%; (diF) , 10%. Example 16 Fluorination of Benzoyl acetone In a similar way to that described in Example 11, fluorine (0.05m) was passed through a solution of benzoyl acetone (0.025m) in 50 ml formic acid over a peiod of 2 hours. The main product was identified by its NMR(CDC1 3 ) [ 19 F, δ F = -190.1 ppm (d) , J HF = 50.0 H\ (keto) and -170.5 ppm (s) (enol) ] and mass spectra [(El) 180 (M + ), 105(C 6 H 5 CO), 77(C 6 H 5 )] as l-phenyl-3-fluoro-2,4- pentanedione. Also formed were compounds in which fluorine had attached the aromatic ring.

Claims: Claims 1. A method for the production of 1, 3-diketones and 1,3- ketoesters of formula (1), (2) or (3) as follows: R 1 COCFR 2 COR 3 (1) (CH 2 ) n COCFCOR 3 (2) ( COCH 3 (4) which comprises converting the corresponding compound of formula (5) , (6) , (7) or (8) as follows: R-LCOCHR2COR3 (5) (CH 2 ) n COCHCOR 3 (6) J (CR 4 R 5 ) n COCHR 2 CO (7) (CR 4 R 5 ) n -CH.CO.CH 3 (8) I I 0 CO into compounds of formula (1) , (2) , (3) or (4) by reaction with elemental fluorine, wherein R-^ is selected from alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl and acetoxy, R 2 is selected from hydrogen, halogen, nitro, cyano, alkyl, cycloalkyl, acetoxy and aryl substituted alkyl, acetoxy, aryl and substituted aryl, and R 3 is selected from alkyl, substituted alkyl, oxyalkyl and substituted oxyalkyl, R 4 and R 5 are hydrogen or alkyl n is an integer in the inclusive range 1 to 8 and the structures represented by formula (2), (3), (4), (6), (7) and (8) are cyclic. 2. A method as in Claim 1 and wherein R 2 in formula (5) or formula (7) is hydrogen, R 2 in formula (1) or formula (3) is fluorine and the product has formula (9) or (10) as follows: R-LC0CF---C0R-3 (9) (CR 4 R 5 ) n COCF 2 CO (10) 3. A method as i Claim 1 or Claim 2 and substantially the same as any one of the Examples described hereinbefore.

Inventors: CHAMBERS RICHARD DICKINSON, GREENHALL MARTIN PAUL, HUTCHINSON JOHN, MOILLIET JOHN STEWART, THOMSON JULIE, CHAMBERS, RICHARD, DICKINSON, GREENHALL, MARTIN, PAUL, HUTCHINSON, JOHN, MOILLIET, JOHN, STEWART, THOMSON, JULIE
Applicants: BNFL FLUORCHEM LTD, CHAMBERS RICHARD DICKINSON, GREENHALL MARTIN PAUL, HUTCHINSON JOHN, MOILLIET JOHN STEWART, THOMSON JULIE, BNFL FLUOROCHEMICALS LTD, CHAMBERS, RICHARD, DICKINSON, GREENHALL, MARTIN, PAUL, HUTCHINSON, JOHN, MOILLIET, JOHN, STEWART, THOMSON, JULIE
Application year: 1994
Main classification: C07B39
IPC codes: C07B39, C07C45, C07C67, C07D307